Internal combustion engines require a higher proportion of fuel in the fuel/air mixture produced in the carburetor (enrichment) during engine start-up cranking speeds to provide easier starting of the engine. Currently, in standard internal combustion engines there are two primary methods of providing the correct fuel enrichment during start-up.
The first method is by the manual or electrical activation of a choke plate. The choke plate is located within the intake bore of the carburetor and can be opened or closed to allow the desired amount of air to flow into the intake bore. When opened, the choke plate completely opens the intake bore and allows the air to flow therethrough. When closed, the choke plate blocks the intake bore except for holes in the choke plate, which have sufficient area to allow a predetermined amount of air to flow into the intake bore to create proper enrichment for start-up.
One drawback to this method of fuel enrichment is that it requires operator interaction. If an engine is difficult to start, the operator must close the choke plate completely to properly enrich the engine for startup. If the choke plate is not completely closed there may not be enough fuel provided to the carburetor and the engine will continue to be difficult to start. In addition, once the engine is running, the operator must remember to open the choke plate or the engine will continue to run in the enriched condition which leads to rough running. A second drawback to this method of fuel enrichment is that it can also be prone to over enrichment, such as if the some or all of the holes in the choke plate become blocked, or under enrichment, such as if the choke plate is not completely closed. Over enrichment can cause hard starting and/or plug fouling.
The second method is by manual or electrical activation of a primer bulb. The primer bulb is typically integral to the carburetor body or remotely mounted to the engine assembly. When the primer bulb is pumped, air or fuel pressure is forced into the fuel circuit pushing the fuel into the carburetor throttle bore.
However, each of these methods have their own particular drawbacks. The first main drawback with the old methods of fuel enrichment is that operator interaction is required. When manually activated both of the above methods can result in not enough fuel being provided to the carburetor and therefore cause difficulty in start-up. The second main drawback is that both of the above methods are prone to over enrichment causing hard starting and/or plug fouling or under enrichment. Both of which prevent easy starting of the engine.
It would therefore be advantageous if a fuel enrichment system for a carburetor of an internal combustion engine could be designed that does not require operator interaction and avoids the problem of over or under enrichment.